1. Field of the Invention
The present invention relates generally to digital video and audio recording and reproduction, and more particularly, to the digital recording/reproduction of compressed audio/video with superimposed sub-information such as subtitles.
2. Description of the Related Art
In one approach to superimposing graphics data representing sub-images (e.g., subtitles) with main information containing digitally encoded motion picture video and audio, the main information and graphics data are time multiplexed and then recorded. Typically, MPEG (Motion Picture Experts Group) encoding is employed to compress the main information as well as the graphics data. With the MPEG technique, encoded data is organized into data blocks referred to as xe2x80x9caccess unitsxe2x80x9d. Within each access unit there is stored reproduction timing information representing the time at which both the main information and the superimposed graphics data of that access unit are to be output for reproduction.
A drawback of the above-noted traditional technique resides in its inherent inefficiency in certain situations. For instance, if correction of just the sub-image data (xe2x80x9csub-informationxe2x80x9d) is desired, then all data subsequent to and including the sub-information for correction has to be isolated and then once again multiplexed after the correction is performed. Moreover, the storage of the reproduction timing information within each access unit is a cause for inefficiency when it is desired to start reproduction (playback) of the stored video program from a user-selected in-progress point of the program, i.e., a point other than the beginning of the program. That is, it becomes necessary to search for the location of the access unit corresponding to the reproduction start time of the selected in-progress point.
In view of the above-noted problems, it is an object of the present invention to provide a way to enable corrections to be made to main information and/or sub-information without the main and sub-information affecting one another.
It is another object of the invention to facilitate the retrieval of reproduction timing information in a digitally compressed audio/video program containing sub-information.
It is a general object of the invention to provide an improved digital video recording/reproduction device and method.
In an illustrative embodiment of the present invention, there is provided an apparatus and method for recording and reproducing audio/video data and graphics data representing sub-images such as subtitles to be superimposed with main images of the video data. Main data comprised of the video and audio data are compression encoded, multiplexed and recorded on a record medium such as an optical or magnetic disk. The graphics data are arranged in at least one file separate from the main data, and separately recorded on the record medium. During reproduction, the graphics data file is read from the record medium at different times than the main data, and buffered separately. The arrangement and recording of the graphics data in its own file(s) simplifies editing and playback operations.
Preferably, a graphics header file is also created and stored separately from the main data, and separately from the file(s) containing the graphics data. The graphics header file contains information relating to the graphics data, such as presentation times at which individual pages of the graphics data are to be decoded and displayed, and arrival times at which the pages are to arrive at a code buffer for temporary storage prior to being displayed. Another file may also be stored on the record medium, which file contains read times at which the pages are to be read from the record medium.